KNX/EIB is a popular standard in building automation. EIBsec is an extension to this standard and supports secure communication. Its concepts are required to implement KNX/EIB in security critical applications like access control and security alarm systems. The performance of KNX/EIB and its extension EIBsec will be analysed by building a simulation. Frameworks for such a simulation will be compared to each other. Furthermore, the simulation framework OMNeT++, which allows the building of a KNX/EIB based network, will be presented in detail. The modelling of the object structure takes special care of the extensibility of the KNX/EIB network. In particular, the implementation analyses the change in network behaviour when an existing KNX/EIB installation is extended with EIBsec.